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<p class="MsoPlainText">This week’s John Anderson Physics Colloquium will be given by Roddy Vann (York). Tea and coffee will be served afterwards as usual.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Speaker: Dr Roddy Vann, Department of Physics, University of York<o:p></o:p></p>
<p class="MsoPlainText">Time/Date: 3pm Wednesday 25<sup>th</sup> March 2015<o:p></o:p></p>
<p class="MsoPlainText">Venue: JA3.14<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Title: The emission, propagation and scattering of microwaves by fusion plasmas<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Abstract:<o:p></o:p></p>
<p class="MsoPlainText">Nuclear fusion offers the possibility of carbon-free energy with an almost limitless fuel supply. Tokamak experiments have made great progress in confinement of plasmas with temperatures in the keV range, necessary to make fusion power
a reality. Diagnosing these plasmas is becoming increasingly challenging as we move towards a reactor due to the large number of high energy neutrons that are produced by the fusion reactions. Microwave diagnostics can be constructed from the same radiation-resilient
materials as the vacuum vessel and are therefore unusually well-suited to installation on a reactor. It is therefore prudent to maximise the diagnostic possibilities based on emitted or reflected microwave radiation.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">One such diagnostic is the Synthetic Aperture Microwave Imaging (SAMI) system that was installed on MAST at the UK’s Culham Centre for Fusion Energy and is currently being transferred to the newly upgraded NSTX tokamak at the Princeton
Plasma Physics Laboratory. This diagnostic uses an array of independently-phased antennas to create, for the first time, a 2-D microwave image of the tokamak plasma. Imaging the spontaneous emission has allowed us to infer some of the physics behind edge-localised
modes (ELMs), which limit the tokamak performance. By imaging the back-scattered signal, we have demonstrated a novel technique for directly measuring the magnetic field in the plasma edge, which is important for understanding the plasma’s stability.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">The tokamak plasma edge is strongly turbulent and we have developed simulation tools to calculate how this turbulent layer scatters the incident microwave signal: these results will also be discussed; an example is shown at this link:
<a href="https://www.youtube.com/watch?v=5b4MN-xnBVw">https://www.youtube.com/watch?v=5b4MN-xnBVw</a><o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoNormal"><a href="http://www.strath.ac.uk/physics/research/colloquia/">http://www.strath.ac.uk/physics/research/colloquia/</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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